Reinforced mineral core for fire doors

ABSTRACT

A mineral core for a door includes a substantially planar slab having a front face, a rear face, and top, bottom and side edges; a plurality of grooves formed in at least one of said front and rear faces, each groove having a reinforcing strip secured therein.

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] This invention relates to doors of wood or timber construction, and particularly to fire rated doors having mineral cores.

[0002] It is well known to incorporate inorganic minerals into the cores of fire doors of wood construction to obtain better resistance to fire. The typical construction of a wood door includes a mineral core with stiles and rails applied along the side and top and bottom edges, respectively, of the mineral core. The core is then interlocked by gluing the core between two outer layers of, for example, plywood, MDF-boards, HDF-boards, polylaminates or other organic cover skins. Hardwood trim and edging or lipping are then typically applied along the edges of the door.

[0003] One problem with lightweight timber fire door cores has been an inability to obtain sufficient strength in the core to resist a hose stream test, immediately following a fire test. The inner lightweight mineral core material in particular has demonstrated weakness, i.e., cracking, resulting in failure of the tests.

[0004] The present invention relates to the incorporation of at least one and preferably a plurality of reinforcing strips in the surface of the lightweight core material to substantially increase the resistance of the core to the fire hose stream according to UL10C and UBC7-2-97. Preferably, the reinforcing strips are oriented parallel to the core side edges, i.e., so that the strips run from top to bottom of the core.

[0005] To achieve resistance to the fire hose stream, especially after 45 or more minutes, the present invention in one exemplary embodiment secures a plurality of reinforcing strips into grooves, via suitable adhesive, on at least one of the front and rear surfaces of the lightweight core material. It will be appreciated, however, that the reinforcing strips can be applied to both sides of the core to obtain an even more rigid and stronger core. The strips themselves may consist of rigid or reinforced material of organic or inorganic origin.

[0006] The door core construction may be formed by press fitting the reinforcing strips within the preformed grooves in the surface of one or both of the rear and front surfaces or faces of the lightweight core material. This can be done sequentially or simultaneously on both sides. The adhesive used to secure the strips to the core may be cement, colloidal matter, inorganic or organic glue. The preferred fixing agent or adhesive is an inorganic silicate glue.

[0007] Accordingly, in its broader aspects, the present invention relates to a mineral core for a door comprising a substantially planar slab having a front face, a rear face, and top, bottom and side edges; and a plurality of grooves formed in at least one of the front and rear faces, each groove having a reinforcing strip secured therein.

[0008] In another aspect, the invention relates to a reinforced door construction comprising a core including a substantially planar slab having a front face, a rear face and top, bottom and side edges with rails along the top and bottom edges and stiles along the side edges; a plurality of grooves formed in at least one of the front face and the rear face; and a reinforcing strip pressed into each of the grooves.

[0009] A detailed description of the invention, utilizing reference numerals keyed to the various figures, is provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a front elevation of a core construction for a door in accordance with one exemplary embodiment of the invention.

[0011]FIG. 2 is a cross section of the core taken through the line 2-2 in FIG. 1;

[0012]FIG. 3 is an enlarged detail taken from FIG. 2;

[0013]FIG. 4 is a cross section of the core taken through the line 4-4 in FIG. 1;

[0014]FIG. 5 is an enlarged detail taken from FIG. 4;

[0015]FIG. 6 is an exploded front elevation of a core construction in accordance with an alternative embodiment of the invention; and

[0016]FIG. 7 is another exploded front elevation of a core construction in accordance with another alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0017] With reference to FIGS. 1-5, one exemplary embodiment of the invention includes a reinforced core construction 10 for a fire resistant door that is made up of a lightweight mineral core 12 having a front surface or face 14 and a rear surface or face 16. Along the sides of the core, stiles 18 are fixed to the core edges and typically include a dense mineral stile 20 and a timber trim strip 22 (FIG. 5). Upper and lower rails 24 include similar dense mineral rails 26, and timber trim strips 28, similar to the stiles 18. The stiles 18 and rails 24 are preferably glued to the inner, lightweight core. The core 12 may be made of lightweight gypsum, low density calcium silicate slabs, vermiculite slabs, perlite slabs, lightweight castable, micro porous slabs or glass bobble slabs. The core 12 is formed with a plurality of longitudinally extending grooves 30 (FIG. 3) that are parallel to the stiles 18, and in laterally spaced relationship along the width of the core. The grooves 30 extend from top to bottom of the core, on at least one of the front and rear faces 14 or 16 of the core. Press fit within the grooves are reinforcing strips 32. Each strip 32 is preferably about ⅞ inch wide (20 mm) and ⅛ inch (3 mm) thick and is press fit and glued into a respective groove 30 that is formed of slightly lesser width and thickness dimensions.

[0018] The strips 32 are made, preferably, of rigid or reinforced material of either organic or inorganic origin. Suitable materials include wood, polylaminate, MDF boards, HDF boards or other organic reinforced strips. Inorganic strips may include glass fiber strips, ceramic fiber strips, ceramic paper, glass fibers, ceramic fibers or paper in a matrix bonded by cement, magnesia cement, colloidal silica, colloidal alumina, potassium silicate, sodium silicate or other inorganic binders.

[0019] Preferably, an adhesive is applied either to the back of the strip 32 or to the groove 30 in the core 12 to insure good bonding of the strip 32 to the core. Preferred glues or adhesives are of the potassium or sodium silicate type. One such glue is sold under the trade name Skamol S-glue available from Skamol A/S. Other suitable glues include #760 Adhesive available from Vimasco Corp., and Foster Fibrous Adhesive 81-27 available from Foster Products Corporation. Typically, such glues or adhesives are effective at temperatures up to 800° F. or higher.

[0020]FIG. 6 illustrates another embodiment of the invention, where the core 36 is formed with grooves and reinforcing strips 38 on both the front and rear faces of the core. Specifically, FIG. 6 illustrates reinforcing strips 38 on the front face 40 of the core 36, and similar strips 38 (in dotted line) on the rear face of the core, with the strips 38 arranged in a laterally offset configuration on respective opposite faces of the core. It will be appreciated that the strips 38 on opposite faces of the core may also be aligned on the front and rear faces, i.e., each pair lying in a single plane extending through the door, parallel to the side edges and stiles 42. Such an arrangement would appear as shown in FIG. 1. FIG. 6 also illustrates the stiles 42 and rails 44 in exploded form, showing the separate stile components 46, 48 and rail components 50, 52.

[0021] It is also possible, but not necessarily preferred, to extend the reinforcing grooves and reinforcing strips beyond the core and into the upper and lower rails, as shown in FIG. 7. In this alternative embodiment, the core slab 54 is identical to the core slab shown in FIG. 6, but grooves for the reinforcing strips 56 have been extended into the upper and lower rails 58. Specifically, extended groove components 60, 62 have been formed, respectively, in the rail components 64, 66 in order to accommodate the extended-length reinforcing strips 56 on one or both faces of the core slab. Here again, the strips 56 on opposite faces may be aligned or laterally offset. The stiles 68 including components 70, 72 remain as in the previously described embodiments.

[0022] It is also within the scope of this invention to orient the reinforcing strips horizontally across the door between the side edges, i.e., parallel to the top and bottom of the door. The strips could also be incorporated in one or both sides of the door in aligned or offset arrangements as described above. The strips could also extend into the stiles along the side edges if desired.

[0023] In a typical door construction, an outer skin (not shown) comprised of wood, metal or plastic material is applied over the core and over the reinforcing strips.

[0024] Incorporation of the reinforcing strips 32, 38 or 56 into the door core has been found to eliminate or minimize the problem of core cracking during fire tests while also providing sufficient strength to resist the hose stream test following a fire test.

[0025] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

What is claimed is:
 1. A mineral core for a door comprising a substantially planar slab having a front face, a rear face, and top, bottom and side edges; and a plurality of grooves formed in at least one of said front and rear faces, each groove having a reinforcing strip secured therein.
 2. The mineral core of claim 1 wherein said grooves and reinforcing strips extend substantially parallel to said side edges and substantially between said top and bottom edges.
 3. The mineral core of claim 1 wherein each reinforcing strip is press fit in a respective one of said grooves.
 4. The mineral core of claim 3 wherein each reinforcing strip is also adhesively secured within a respective one of said grooves.
 5. The mineral core of claim 1 wherein said reinforcing strips are made of wood, polylaminate, MDF boards or HDF boards.
 6. The mineral core of claim 1 wherein said reinforcing strips are made of glass fiber strips, ceramic fiber strips, glass fibers, ceramic fibers or paper in a matrix bonded by cement, magnesia cement, colloidal silica, colloidal alumina, potassium silicate or sodium silicate.
 7. The mineral core of claim 1 wherein said grooves are formed in both said front and rear faces of said core, with a reinforcing strip in each groove.
 8. The mineral core of claim 7 wherein said respective pairs of grooves on said front and rear faces lie in single planes extending through the core, parallel to said side edges.
 9. The mineral core of claim 7 wherein said grooves on said front and rear faces are laterally offset from each other.
 10. The mineral core of claim 1 wherein grooves are each about ⅞ inch wide and ⅛ inch deep.
 11. The mineral core of claim 4 wherein said adhesive is a potassium or sodium silicate glue.
 12. A reinforced door construction comprising: a core including a substantially planar slab having a front face, a rear face and top, bottom and side edges with rails along said top and bottom edges and stiles along said side edges; a plurality of grooves formed in at least one of said front face and said rear face; and a reinforcing strip pressed into each of said grooves.
 13. The reinforced door construction or claim 12 wherein said reinforcing strips are adhesively secured within said grooves.
 14. The reinforced door of claim 13 wherein said reinforcing strips are made of wood, polylaminate, MDF boards or HDF boards.
 15. The reinforced door of claim 14 wherein said reinforcing strips are made of glass fiber strips, ceramic fiber strips, glass fibers, ceramic fibers or paper in a matrix bonded by cement, magnesia cement, colloidal silica, colloidal alumina, potassium silicate or sodium silicate.
 16. The reinforced door of claim 12 wherein said grooves are formed in both said front and rear faces of said core, with a reinforcing strip in each groove.
 17. The reinforced door of claim 16 wherein said respective pairs of grooves on said front and rear faces lie in single planes extending through the core, parallel to said side edges.
 18. The reinforced door of claim 16 wherein said grooves on said front and rear faces are laterally offset from each other.
 19. The reinforced door of claim 12 wherein grooves are each about ⅞ inch wide and ⅛ inch deep.
 20. The reinforced door of claim 13 wherein said adhesive is a potassium or sodium silicate glue.
 21. The reinforced door of claim 12 wherein said grooves and reinforcing strips extend into said rails.
 22. The reinforced door of claim 12 wherein said grooves extend substantially parallel to said side edges, at least between said top and bottom edges of said core. 